I. Field of the Invention
This invention generally relates to microscopy and spectroscopy. More particularly, the present invention pertains to a microscope for use in molecular microspectrometry using infrared radiant energy.
II. Description of the Related Art
The spatial resolution from conventional microscope-spectrometer combinations is limited by the relatively long wavelength (.lambda.) of infrared radiation. For example, the diffraction limited spatial resolution (d) for a microscope with a limiting numerical aperture (N.A.) is d=(0.62.lambda./N.A.). For analyzing molecular compounds such as organic substances, certain ionic salts and silicate minerals, radiant energy in the mid-infrared range of 2.5 to 25 .mu.m is most useful. In this mid-infrared spectral range, the conventional diffraction limited spatial resolution is about 10 .mu.m.
In the field of light microscopy, there has been a steady progression away from fixed tube-length optical designs to infinity corrected microscopes. An infinity corrected microscope objective lens produces a nearly collimated beam of light from a sample. Viewing this collimated beam with a telescopic optical system produces a magnified image of the sample. Infinity corrected microscope optical designs have the advantage of allowing the placement of various optical elements in the collimated beam without degrading image quality.
Confocal apertures were first applied to infrared microspectroscopy by Messerschmidt and Sting to improve spatial resolution as is disclosed in U.S. Pat. No. 4,877,960. In this development, a pair of matched dual remote image plane masks or apertures were used to achieve the confocal geometry, as introduced by Minsky and explained in U.S. Pat. No. 3,013,467. On closer inspection, it was discovered that the separate masks or apertures were only required in a transmission mode for transmissive analysis. In a reflection mode for reflective analysis, however, use of a single aperture produces the confocal effect by defining both the area of the sample illuminated with radiant energy from the source, and the area of the sample reflecting radiant energy to the detector. The dual function of the sample defining aperture in reflection microspectrometry is common to several earlier designs.
For transmissive analysis with confocal sample defining masks, prior art systems require dual remote apertures having equal size images and the same geometrical shape at a sample plane. The infrared light used to radiate the transparent sample is masked twice; the first masking occurs before the light is incident to the surface of the sample such as when the light is travelling from a light source to the sample, and the second masking occurs after the radiant energy transmissively exits from the sample, i.e. when the light is travelling from the sample to a visible and/or infrared light detector.
The need for two separate apertures for transmission microspectrometry adds complexity and cost. For example, to properly operate such a system the user must align and match both the size and orientation of the two separate remote apertures as well as bring them both to a common focus. In addition, technical skills are required to adjust sample masks. As a result of the problems associated with dual remote aperture systems, many commercial microspectrometers have elected to employ single aperture systems for transmission measurements wherein the radiation signal travels through the aperture only once, i.e. in a direction from a radiation source to a sample, thus yielding simplicity of operation while sacrificing resolution.
Another drawback of existing microspectrometers is the inability to provide simultaneous visual observation of an object image while measuring or detecting the infrared light. For example, in many prior art systems, including the system described in commonly owned U.S. Pat. No. 5,581,085, a reflecting element (shown as element 24 in FIG. 1 of U.S. Pat. No. 5,581,085) must be removed from the path of the reflected or transmitted light so that the visible light is viewable by a user or a visible light detector, such as a video camera. When infrared measurements are needed, however, the reflecting element must be re-positioned in the light path of the irradiated sample so that the infrared light is reflected back to a detector. When so positioned, visible image observation is no longer available, thus making continuous automatic focusing features difficult, if not impossible, to implement.
A further drawback of prior art microspectrometer systems is that for an automated sequence of spectral measurements, the size or area of the dual apertures used to mask an object and to control the amount of light is fixed. Since the masked area of the sample cannot be varied during an automated spectral collection sequence, optimum sample masking is sacrificed. For example, if a sequence of particulates or cells were to be analyzed sequentially in an automated fashion, the prior art would require that the dual remote apertures be sized to the smallest feature and this size could not be changed during the sequence.
Still a further drawback of prior art microspectrometer systems is that they only accommodate and direct infrared light back to a single detector unit. If a different detector unit is desired, such as to obtain analyses other than those capable of being rendered by a first detector, the first detector must be disconnected or otherwise removed from an output light path and another detector substituted therefor.
Accordingly, it is an object of the present invention to provide a microscope using a single confocal aperture for transmission and reflection microspectrometry wherein during a transmission mode of operation, radiant energy passes through the aperture in a first and a second direction.
It is a further object of the present invention to provide a microscope having simultaneous visible image observation and infrared detection features so that an object image can be observed while infrared measurements are obtained and which provides a means for continuous adjustment of the sample focus by a focusing means.
It is still a further object of the present invention to provide a microscope having a mechanism for adjusting and regulating the area of a single confocal aperture to vary the radiated area of a subject sample.
It is another object of the present invention to provide a microscope accommodating multiple detectors and for selectively directing infrared light therebetween.
It is yet another object of the present invention to provide detector mounting platforms capable of three-dimensional movement for aligning a detector with an output infrared beam emanating from the microscope.